Five areas of theoretical population genetic research are to be developed. The effect on the sex ratio of linkage between genes that interact in determining sex is to be explored in diploid and haplodiploid systems. In addition, the consequences for the sex ratio of population subdivision and migration are to be studied. Research on the evolution of genetic modifiers of the rate of recombination will be continued with particular reference to populations subject to fertility selection or in which the sexes differ in their viabilities. New studies of the evolution of recombination modifiers in small populations are to be initiated. Our studies of cultural transmission and evolution will attempt to relate predictions from dynamic transmission models to commonly used data analytic techniques. In addition, we shall pursue studies of population genetic models for the evolution of communication. Demographic modelling of culturally transmitted traits will be introduced, with the transmission rate depending on the ages of the transmitter and receiver. Finally, we propose to examine how, in a large subdivided population, levels of clustering of subpopulations affect estimates of spatial variation in gene frequencies.